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IEM FFT scan

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Cliff Fuller:
I have two IEM systems and I have done an FFT scan of the radio outputs. There is no audio to the inputs of the transmitters. What is the difference that I am seeing? What is the cause of the apparent distortion?

Thanks...

Henry Cohen:

--- Quote from: Cliff Fuller on January 31, 2023, 04:35:03 PM ---I have two IEM systems and I have done an FFT scan of the radio outputs. There is no audio to the inputs of the transmitters. What is the difference that I am seeing? What is the cause of the apparent distortion?
--- End quote ---

Concerning the second image of 486MHz: What is the span?

Concerning both images, please specify measurement parameters for each:
RBW
VBW
Window type
Detector
Averaging

Cliff Fuller:

--- Quote from: Henry Cohen on January 31, 2023, 08:24:48 PM ---Concerning the second image of 486MHz: What is the span?

Concerning both images, please specify measurement parameters for each:
RBW
VBW
Window type
Detector
Averaging

--- End quote ---

Good evening, Henry.
I'll do my best to answer your questions. Prefacing those answers, I'm using an RTL-SDR USB dongle to do the scans and using an application called "GQRX" as the tuner. I will apologize that I'm not an RF engineer so I'm having a bit of a challenge translating your questions.

Both images were grabbed under the same circumstances. No other transmitters were powered on at the time of measurement. I think the answers are as follows:

span: 2.5 MHz
RBW: 293.0 Hz
VBW: 2.5 Mhz
Window type: hamming
Detector: ?
Averaging: 85%

Thanks for the look and any insight given.

Jerome Malsack:
roughly guessing   that one might be a digital transmitter and the other could be  old school FM ??   upper and lower side bands and the noise floor. 

Cliff Fuller:

--- Quote from: Jerome Malsack on February 01, 2023, 11:01:19 AM ---roughly guessing   that one might be a digital transmitter and the other could be  old school FM ??   upper and lower side bands and the noise floor.

--- End quote ---

The transmitters are a pair of PSM 900s. There are a total of 6, the 504 MHz seems to be the only one without the added "noise". They have been in service for about 10 years. There doesn't seem to be any audible degradation.

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